Buffer Overflows Public Enemy Number 1

Total Page:16

File Type:pdf, Size:1020Kb

Buffer Overflows Public Enemy Number 1 Software Security Buffer Overflows public enemy number 1 Erik Poll Digital Security Radboud University Nijmegen The good news C is a small language that is close to the hardware • you can produce highly efficient code • compiled code runs on raw hardware with minimal infrastructure C is typically the programming language of choice • for highly efficient code • for embedded systems (which have limited capabilities) • for system software (operating systems, device drivers,...) 2 The bad news : using C(++) is dangerous 3 Essence of the problem Suppose in a C program we have an array of length 4 char buffer[4]; What happens if we execute the statement below ? buffer[4] = ‘a’; This is UNDEFINED! ANYTHING can happen ! If the data written (ie. the “a”) is user input that can be controlled by an attacker, this vulnerability can be exploited: anything that the attacker wants can happen. 4 Solution to this problem • Check array bounds at runtime – Algol 60 proposed this back in 1960! • Unfortunately, C and C++ have not adopted this solution, for efficiency reasons. (Perl, Python, Java, C#, and even Visual Basic have) • As a result, buffer overflows have been the no 1 security problem in software ever since 5 Problems caused by buffer overflows • The first Internet worm, and all subsequent ones (CodeRed, Blaster, ...), exploited buffer overflows • Buffer overflows cause in the order of 50% of all security alerts – Eg check out CERT, cve.mitre.org, or bugtraq • Trends – Attacks are getting cleverer • defeating ever more clever countermeasures – Attacks are getting easier to do, by script kiddies 6 Any C(++) code acting on untrusted input is at risk • code taking input over untrusted network – eg. sendmail, web browser, wireless network driver,... • code taking input from untrusted user on multi-user system, – esp. services running with high privileges (as ROOT on Unix/Linux, as SYSTEM on Windows) • code acting on untrusted files – that have been downloaded or emailed • also embedded software - eg. in devices with (wireless) network connections such as mobile phones, RFID card, airplane navigation systems, ... 7 How does buffer overflow work? Memory management in C/C++ • A program is responsible for its memory management • Memory management is very error-prone – Who here has had a C(++) program crash with a segmentation fault? Technical term: C and C++ do not offer memory-safety • Typical bugs: – Writing past the bound of an array – Pointer trouble • missing initialisation, bad pointer arithmetic, use after de- allocation (use after free), double de-allocation, failed allocation, forgotten de-allocation (memory leaks)... • For efficiency, these bugs are not detected at run time: – behaviour of a buggy program is undefined 9 Process memory layout High Arguments/ Environment Stack grows addresses down, Stack by procedure calls Unused Memory Heap (dynamic data) Heap grows up, eg. by malloc Static Data .data and new Low addresses Program Code .text 10 Stack overflow The stack consists of Activation Records: x AR main() return address AR f() buf[4..7] buf[0..3] void f(int x) { Stack grows Buffer grows char[8] buf; downwards upwards gets(buf); } void main() { f(…); … } void format_hard_disk(){…} 11 Stack overflow What if gets() reads more than 8 bytes ? : x AR main() return address AR f() buf[4..7] buf[0..3] void f(int x) { Buffer grows char[8] buf; upwards gets(buf); } void main() { f(…); … } void format_hard_disk(){…} 12 Stack overflow What if gets() reads more than 8 bytes ? x AR main() return address AR f() buf[4..7] buf[0..3] void f(int x) { Buffer grows char[8] buf; upwards gets(buf); } void main() { f(…); … } void format_hard_disk(){…} 13 Stack overflow What if gets() reads more than 8 bytes ? x AR main() return address AR f() buf[4..7] buf[0..3] void f(int x) { Stack grows Buffer grows char[8] buf; downwards upwards gets(buf); } never use void main() { gets()! f(…); … } void format_hard_disk(){…} 14 Stack overflow • How the attacks works: overflowing buffers to corrupt data • Lots of details to get right: – No nulls in (character-)strings – Filling in the correct return address: • Fake return address must be precisely positioned • Attacker might not know the address of his own string – Other overwritten data must not be used before return from function – … • Variant: Heap overflow of a buffer allocated on the heap instead of the stack 15 What to attack? Fun with the stack void f(char* buf1, char* buf2, bool b1) { int i; bool b2; void (*fp)(int); char[] buf3; .... } Overflowing stack-allocated buffer buf3 to • corrupt return address – ideally, let this return address point to another buffers where the attack code is placed • corrupt function pointers, such as fp • corrupt any other data on the stack, eg. b2, i, b1, buf2,.. ... What to attack? Fun on the heap struct account { int number; bool isSuperUser; char name[20]; int balance; } overrun name to corrupt the values of other fields in the struct What causes buffer overflows? Example: gets char buf[20]; gets(buf); // read user input until // first EoL or EoF character • Never use gets • Use fgets(buf, size, stdin) instead 19 Example: strcpy char dest[20]; strcpy(dest, src); // copies string src to dest • strcpy assumes dest is long enough , and assumes src is null-terminated • Use strncpy(dest, src, size) instead 20 Spot the defect! (1) char buf[20]; char prefix[] = ”http://”; ... strcpy(buf, prefix); // copies the string prefix to buf strncat(buf, path, sizeof(buf)); // concatenates path to the string buf 21 Spot the defect! (1) char buf[20]; char prefix[] = ”http://”; ... strcpy(buf, prefix); // copies the string prefix to buf strncat(buf, path, sizeof(buf)); // concatenates path to the string buf strncat’s 3rd parameter is number of chars to copy, not the buffer size Another common mistake is giving sizeof(path) as 3rd argument... 22 Spot the defect! (2) char src[9]; char dest[9]; char* base_url = ”www.ru.nl”; strncpy(src, base_url, 9); // copies base_url to src strcpy(dest, src); // copies src to dest 23 Spot the defect! (2) base_url is 10 chars long, incl. its char src[9]; null terminator, so src will not be char dest[9]; null-terminated char* base_url = ”www.ru.nl”; strncpy(src, base_url, 9); // copies base_url to src strcpy(dest, src); // copies src to dest 24 Spot the defect! (2) base_url is 10 chars long, incl. its char src[9]; null terminator, so src will not be char dest[9]; null-terminated char* base_url = ”www.ru.nl”; strncpy(src, base_url, 9); // copies base_url to src strcpy(dest, src); // copies src to dest so strcpy will overrun the buffer dest 25 Example: strcpy and strncpy • Don’t replace strcpy(dest, src) by strncpy(dest, src, sizeof(dest)) but by strncpy(dest, src, sizeof(dest)-1) dst[sizeof(dest)-1] = `\0`; if dest should be null-terminated! • Btw: a strongly typed programming language could of course enforce that strings are always null-terminated... 26 Spot the defect! (3) char *buf; int i, len; read(fd, &len, sizeof(int)); // read sizeof(int) bytes, ie. an int, // and store these in len buf = malloc(len); read(fd,buf,len); // read len bytes into buf 27 Spot the defect! (3) char *buf; len might become negative int i, len; read(fd, &len, sizeof(int)); // read sizeof(int) bytes, ie. an int, // and store these in len buf = malloc(len); read(fd,buf,len); // read len bytes into buf len cast to unsigned, so negative length overflows read then goes beyond the end of buf 28 Spot the defect! (3) char *buf; int i, len; read(fd, &len, sizeof(len)); if (len < 0) {error ("negative length"); return; } buf = malloc(len); read(fd,buf,len); Remaining problem may be that buf is not null-terminated 29 Spot the defect! (3) char *buf; May result in integer overflow; int i, len; we should check that len+1 is positive read(fd, &len, sizeof(len)); if (len < 0) {error ("negative length"); return; } buf = malloc(len+1); read(fd,buf,len); buf[len] = '\0'; // null terminate buf 30 Spot the defect! (5) #define MAX_BUF 256 void BadCode (char* input) { short len; char buf[MAX_BUF]; len = strlen(input); if (len < MAX_BUF) strcpy(buf,input); } 31 Spot the defect! (5) #define MAX_BUF 256 What if input is longer than 32K ? void BadCode (char* input) { short len; len will be a negative number, char buf[MAX_BUF]; due to integer overflow len = strlen(input); hence: potential buffer overflow if (len < MAX_BUF) strcpy(buf,input); } The integer overflow is the root problem, but the (heap) buffer overflow that this enables make it exploitable 32 Spot the defect! (4) #ifdef UNICODE #define _sntprintf _snwprintf #define TCHAR wchar_t #else #define _sntprintf _snprintf #define TCHAR char #endif TCHAR buff[MAX_SIZE]; _sntprintf(buff, sizeof(buff), ”%s\n”, input); [slide from presentation by Jon Pincus] 33 Spot the defect! (4) #ifdef UNICODE #define _sntprintf _snwprintf #define TCHAR wchar_t #else #define _sntprintf _snprintf #define TCHAR char nd #endif _sntprintf’s 2 param is # of chars in buffer, not # of bytes TCHAR buff[MAX_SIZE]; _sntprintf(buff, sizeof(buff), ”%s\n”, input); The CodeRed worm exploited such an mismatch: code written under the assumption that 1 char was 1 byte allowed buffer overflows after the move from ASCI to Unicode [slide from presentation by Jon Pincus] 34 Spot the defect! (6) bool CopyStructs(InputFile* f, long count) { structs = new Structs[count]; for (long i = 0; i < count; i++) { if !(ReadFromFile(f,&structs[i]))) break; } } 35 Spot the defect! (6) bool CopyStructs(InputFile* f, long count) { structs = new Structs[count]; for (long i = 0; i < count; i++) { if !(ReadFromFile(f,&structs[i]))) break; } } effectively does a malloc(count*sizeof(type)) which may cause integer overflow And this integer overflow can lead to a (heap) buffer overflow.
Recommended publications
  • Tesi Final Marco Oliverio.Pdf
    i Abstract Advancements in exploitation techniques call for the need of advanced defenses. Modern operating systems have to face new sophisticate attacks that do not rely on any programming mistake, rather they exploit leaking information from computational side effects (side-channel attacks) or hardware glitches (rowhammer attacks). Mitigating these new attacks poses new challanges and involves delicate trade-offs, balancing security on one side and performance, simplicity, and compatibility on the other. In this disseration we explore the attack surface exposed by page fusion, a memory saving optimization in modern operating systems and, after that, a secure page fusion implementation called VUsion is shown. We then propose a complete and compatible software solution to rowhammer attacks called ZebRAM. Lastly, we show OpenCAL, a free and general libray for the implementation of Cellular Automata, that can be used in several security scenarios. iii Acknowledgements I would like to thank my Supervisor prof. Andrea Pugliese for the encouragement and the extremely valuable advice that put me in a fruitful and exciting research direction. A hearty acknowledgment goes to Kaveh Razavi, Cristiano Giuffrida, Herbert Bos and all the VUSec group of the Vrije Universiteit of Amsterdam. I felt at home from day one and I found myself surrounded by brilliant researchers and good friends. v Contents Abstract i Acknowledgements iii Introduction1 1 VUsion3 1.1 Introduction...................................3 1.2 Page Fusion...................................5 1.2.1 Linux Kernel Same-page Merging...................5 1.2.2 Windows Page Fusion.........................7 1.3 Threat Model..................................8 1.4 Known Attack Vectors.............................8 1.4.1 Information Disclosure.........................8 1.4.2 Flip Feng Shui.............................9 1.5 New Attack Vectors..............................
    [Show full text]
  • An In-Depth Study with All Rust Cves
    Memory-Safety Challenge Considered Solved? An In-Depth Study with All Rust CVEs HUI XU, School of Computer Science, Fudan University ZHUANGBIN CHEN, Dept. of CSE, The Chinese University of Hong Kong MINGSHEN SUN, Baidu Security YANGFAN ZHOU, School of Computer Science, Fudan University MICHAEL R. LYU, Dept. of CSE, The Chinese University of Hong Kong Rust is an emerging programing language that aims at preventing memory-safety bugs without sacrificing much efficiency. The claimed property is very attractive to developers, and many projects start usingthe language. However, can Rust achieve the memory-safety promise? This paper studies the question by surveying 186 real-world bug reports collected from several origins which contain all existing Rust CVEs (common vulnerability and exposures) of memory-safety issues by 2020-12-31. We manually analyze each bug and extract their culprit patterns. Our analysis result shows that Rust can keep its promise that all memory-safety bugs require unsafe code, and many memory-safety bugs in our dataset are mild soundness issues that only leave a possibility to write memory-safety bugs without unsafe code. Furthermore, we summarize three typical categories of memory-safety bugs, including automatic memory reclaim, unsound function, and unsound generic or trait. While automatic memory claim bugs are related to the side effect of Rust newly-adopted ownership-based resource management scheme, unsound function reveals the essential challenge of Rust development for avoiding unsound code, and unsound generic or trait intensifies the risk of introducing unsoundness. Based on these findings, we propose two promising directions towards improving the security of Rust development, including several best practices of using specific APIs and methods to detect particular bugs involving unsafe code.
    [Show full text]
  • Ensuring the Spatial and Temporal Memory Safety of C at Runtime
    MemSafe: Ensuring the Spatial and Temporal Memory Safety of C at Runtime Matthew S. Simpson, Rajeev K. Barua Department of Electrical & Computer Engineering University of Maryland, College Park College Park, MD 20742-3256, USA fsimpsom, [email protected] Abstract—Memory access violations are a leading source of dereferencing pointers obtained from invalid pointer arith- unreliability in C programs. As evidence of this problem, a vari- metic; and dereferencing uninitialized, NULL or “manufac- ety of methods exist that retrofit C with software checks to detect tured” pointers.1 A temporal error is a violation caused by memory errors at runtime. However, these methods generally suffer from one or more drawbacks including the inability to using a pointer whose referent has been deallocated (e.g. with detect all errors, the use of incompatible metadata, the need for free) and is no longer a valid object. The most well-known manual code modifications, and high runtime overheads. temporal violations include dereferencing “dangling” point- In this paper, we present a compiler analysis and transforma- ers to dynamically allocated memory and freeing a pointer tion for ensuring the memory safety of C called MemSafe. Mem- more than once. Dereferencing pointers to automatically allo- Safe makes several novel contributions that improve upon previ- ous work and lower the cost of safety. These include (1) a method cated memory (stack variables) is also a concern if the address for modeling temporal errors as spatial errors, (2) a compati- of the referent “escapes” and is made available outside the ble metadata representation combining features of object- and function in which it was defined.
    [Show full text]
  • Improving Memory Management Security for C and C++
    Improving memory management security for C and C++ Yves Younan, Wouter Joosen, Frank Piessens, Hans Van den Eynden DistriNet, Katholieke Universiteit Leuven, Belgium Abstract Memory managers are an important part of any modern language: they are used to dynamically allocate memory for use in the program. Many managers exist and depending on the operating system and language. However, two major types of managers can be identified: manual memory allocators and garbage collectors. In the case of manual memory allocators, the programmer must manually release memory back to the system when it is no longer needed. Problems can occur when a programmer forgets to release it (memory leaks), releases it twice or keeps using freed memory. These problems are solved in garbage collectors. However, both manual memory allocators and garbage collectors store management information for the memory they manage. Often, this management information is stored where a buffer overflow could allow an attacker to overwrite this information, providing a reliable way to achieve code execution when exploiting these vulnerabilities. In this paper we describe several vulnerabilities for C and C++ and how these could be exploited by modifying the management information of a representative manual memory allocator and a garbage collector. Afterwards, we present an approach that, when applied to memory managers, will protect against these attack vectors. We implemented our approach by modifying an existing widely used memory allocator. Benchmarks show that this implementation has a negligible, sometimes even beneficial, impact on performance. 1 Introduction Security has become an important concern for all computer users. Worms and hackers are a part of every day internet life.
    [Show full text]
  • Buffer Overflows Buffer Overflows
    L15: Buffer Overflow CSE351, Spring 2017 Buffer Overflows CSE 351 Spring 2017 Instructor: Ruth Anderson Teaching Assistants: Dylan Johnson Kevin Bi Linxing Preston Jiang Cody Ohlsen Yufang Sun Joshua Curtis L15: Buffer Overflow CSE351, Spring 2017 Administrivia Homework 3, due next Friday May 5 Lab 3 coming soon 2 L15: Buffer Overflow CSE351, Spring 2017 Buffer overflows Address space layout (more details!) Input buffers on the stack Overflowing buffers and injecting code Defenses against buffer overflows 3 L15: Buffer Overflow CSE351, Spring 2017 not drawn to scale Review: General Memory Layout 2N‐1 Stack Stack . Local variables (procedure context) Heap . Dynamically allocated as needed . malloc(), calloc(), new, … Heap Statically allocated Data . Read/write: global variables (Static Data) Static Data . Read‐only: string literals (Literals) Code/Instructions Literals . Executable machine instructions Instructions . Read‐only 0 4 L15: Buffer Overflow CSE351, Spring 2017 not drawn to scale x86‐64 Linux Memory Layout 0x00007FFFFFFFFFFF Stack Stack . Runtime stack has 8 MiB limit Heap Heap . Dynamically allocated as needed . malloc(), calloc(), new, … Statically allocated data (Data) Shared Libraries . Read‐only: string literals . Read/write: global arrays and variables Code / Shared Libraries Heap . Executable machine instructions Data . Read‐only Instructions Hex Address 0x400000 0x000000 5 L15: Buffer Overflow CSE351, Spring 2017 not drawn to scale Memory Allocation Example Stack char big_array[1L<<24]; /* 16 MB */ char huge_array[1L<<31]; /* 2 GB */ int global = 0; Heap int useless() { return 0; } int main() { void *p1, *p2, *p3, *p4; Shared int local = 0; Libraries p1 = malloc(1L << 28); /* 256 MB */ p2 = malloc(1L << 8); /* 256 B */ p3 = malloc(1L << 32); /* 4 GB */ p4 = malloc(1L << 8); /* 256 B */ Heap /* Some print statements ..
    [Show full text]
  • Memory Vulnerability Diagnosis for Binary Program
    ITM Web of Conferences 7 03004 , (2016) DOI: 10.1051/itmconf/20160703004 ITA 2016 Memory Vulnerability Diagnosis for Binary Program Feng-Yi TANG, Chao FENG and Chao-Jing TANG College of Electronic Science and Engineering National University of Defense Technology Changsha, China Abstract. Vulnerability diagnosis is important for program security analysis. It is a further step to understand the vulnerability after it is detected, as well as a preparatory step for vulnerability repair or exploitation. This paper mainly analyses the inner theories of major memory vulnerabilities and the threats of them. And then suggests some methods to diagnose several types of memory vulnerabilities for the binary programs, which is a difficult task due to the lack of source code. The diagnosis methods target at buffer overflow, use after free (UAF) and format string vulnerabilities. We carried out some tests on the Linux platform to validate the effectiveness of the diagnosis methods. It is proved that the methods can judge the type of the vulnerability given a binary program. 1 Introduction (or both) the memory area. These headers can contain some information like size, used or not, and etc. Memory vulnerabilities are difficult to detect and diagnose Therefore, we can monitor the allocator so as to especially for those do not crash the program. Due to its determine the base address and the size of the allocation importance, vulnerability diagnosis problem has been areas. Then, check all STORE and LOAD accesses in intensively studied. Researchers have proposed different memory to see which one is outside the allocated area. techniques to diagnose memory vulnerabilities.
    [Show full text]
  • A Buffer Overflow Study
    A Bu®er Overflow Study Attacks & Defenses Pierre-Alain FAYOLLE, Vincent GLAUME ENSEIRB Networks and Distributed Systems 2002 Contents I Introduction to Bu®er Overflows 5 1 Generalities 6 1.1 Process memory . 6 1.1.1 Global organization . 6 1.1.2 Function calls . 8 1.2 Bu®ers, and how vulnerable they may be . 10 2 Stack overflows 12 2.1 Principle . 12 2.2 Illustration . 12 2.2.1 Basic example . 13 2.2.2 Attack via environment variables . 14 2.2.3 Attack using gets . 16 3 Heap overflows 18 3.1 Terminology . 18 3.1.1 Unix . 18 3.1.2 Windows . 18 3.2 Motivations and Overview . 18 3.3 Overwriting pointers . 19 3.3.1 Di±culties . 20 3.3.2 Interest of the attack . 20 3.3.3 Practical study . 20 3.4 Overwriting function pointers . 24 3.4.1 Pointer to function: short reminder . 24 3.4.2 Principle . 24 3.4.3 Example . 25 3.5 Trespassing the heap with C + + . 28 3.5.1 C++ Background . 28 3.5.2 Overwriting the VPTR . 31 3.5.3 Conclusions . 32 3.6 Exploiting the malloc library . 33 3.6.1 DLMALLOC: structure . 33 3.6.2 Corruption of DLMALLOC: principle . 34 II Protection solutions 37 4 Introduction 38 1 5 How does Libsafe work? 39 5.1 Presentation . 39 5.2 Why are the functions of the libC unsafe ? . 39 5.3 What does libsafe provide ? . 40 6 The Grsecurity Kernel patch 41 6.1 Open Wall: non-executable stack .
    [Show full text]
  • Buffer Overflow and Format String Overflow Vulnerabilities 3
    Syracuse University SURFACE Electrical Engineering and Computer Science College of Engineering and Computer Science 2002 Buffer Overflow and ormatF String Overflow ulnerV abilities Kyung-suk Lhee Syracuse University Steve J. Chapin Syracuse University Follow this and additional works at: https://surface.syr.edu/eecs Part of the Computer Sciences Commons Recommended Citation Lhee, Kyung-suk and Chapin, Steve J., "Buffer Overflow and ormatF String Overflow ulnerV abilities" (2002). Electrical Engineering and Computer Science. 96. https://surface.syr.edu/eecs/96 This Article is brought to you for free and open access by the College of Engineering and Computer Science at SURFACE. It has been accepted for inclusion in Electrical Engineering and Computer Science by an authorized administrator of SURFACE. For more information, please contact [email protected]. SOFTWARE|PRACTICE AND EXPERIENCE Softw. Pract. Exper. 2002; 00:1{7 Bu®er Overflow and Format String Overflow Vulnerabilities Kyung-Suk Lhee and Steve J. Chapin¤,y Center for Systems Assurance, Syracuse University, Syracuse, NY 13210 SUMMARY Bu®er overflow vulnerabilities are among the most widespread of security problems. Numerous incidents of bu®er overflow attacks have been reported and many solutions have been proposed, but a solution that is both complete and highly practical is yet to be found. Another kind of vulnerability called format string overflow has recently been found, and though not as popular as bu®er overflow, format string overflow attacks are no less dangerous. This article surveys representative techniques of exploiting bu®er overflow and format string overflow vulnerabilities and their currently available defensive measures. We also describe our bu®er overflow detection technique that range checks the referenced bu®ers at run time.
    [Show full text]
  • Chapter 10 Buffer Overflow Buffer Overflow
    Chapter 10 Buffer Overflow Buffer Overflow ● Common attack mechanism ○ first wide use by the Morris Worm in 1988 ● Prevention techniques known ○ NX bit, stack canaries, ASLR ● Still of major concern ○ Recent examples: Shellshock, Hearthbleed Buffer Overflow/Buffer Overrun Definition: A condition at an interface under which more input can be placed into a buffer or data holding area than the capacity allocated, overwriting other information. Attackers exploit such a condition to crash a system or to insert specially crafted code that allows them to gain control of the system. Buffer Overflow Basics ● Programming error when a process attempts to store data beyond the limits of a fixed-sized buffer ● Overwrites adjacent memory locations ○ locations may hold other program variables, parameters, or program control flow data ○ buffer could be located on the stack, in the heap, or in the data section of the process ● Consequences: ○ corruption of program data ○ unexpected transfer of control ○ memory access violations Basic Buffer Overflow Example Basic Buffer Overflow Stack Values Buffer Overflow Attacks Attacker needs: ● To identify a buffer overflow vulnerability in some program that can be triggered using externally sourced data under the attacker’s control ● To understand how that buffer is stored in memory and determine potential for corruption Identifying vulnerable programs can be done by: ● inspection of program source ● tracing the execution of programs as they process oversized input ● using tools such as fuzzing to automatically identify
    [Show full text]
  • Memory Management
    Memory Management Advanced Operating System Lecture 5 Colin Perkins | https://csperkins.org/ | Copyright © 2017 | This work is licensed under the Creative Commons Attribution-NoDerivatives 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nd/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA. Lecture Outline • Virtual memory • Layout of a processes address space • Stack • Heap • Program text, shared libraries, etc. • Memory management Colin Perkins | https://csperkins.org/ | Copyright © 2017 2 Virtual Memory (1) • Processes see virtual addresses – each process believes it has access to the entire address space • Kernel programs the MMU (“memory management unit”) to translate these into physical addresses, representing real memory – mapping changed each context switch to another process Main memory! CPU chip! 0:! Virtual! Address! Physical! 1:! address! translation! address! 2:! (VA)! (PA)! 3:! CPU! MMU! 4:! 4100 4 5:! 6:! 7:! ... ! Source: Bryant & O’Hallaron, “Computer Systems: A Programmer’s Perspective”, 3rd Edition, Pearson, 2016. Fig. 9.2. http://csapp.cs.cmu.edu/ M-1:! 3e/figures.html (website grants permission for lecture use with attribution) Data word! Colin Perkins | https://csperkins.org/ | Copyright © 2017 3 Virtual Memory (2) Virtual address spaces! Physical memory! • Virtual-to-physical memory mapping 0! 0! Address translation! can be unique or shared VP 1! Process i:! VP 2! • Unique mappings typical – physical memory N-1! owned by a single process Shared page! • Shared mappings allow one read-only copy 0! Process j:! VP 1! of a shared library to be accessed by many VP 2! processes N-1! M-1! Source: Bryant & O’Hallaron, “Computer Systems: A Programmer’s Perspective”, • Memory protection done at page level – each 3rd Edition, Pearson, 2016.
    [Show full text]
  • Table of Contents
    Table of Contents Cybersecurity and Cyber Systems........................................................................1 Cybersecurity and Cyber Systems The Master of Science degree in Cybersecurity and Cyber Systems is an interdisciplinary program offered through the School of Computing and the School of Electrical, Computer, and Biomedical Engineering. Master of Science (M.S.) in Cybersecurity and Cyber Systems Admission Applicants with a bachelors degree in Computer Science, Engineering, Physics, Mathematics, Information Systems or equivalent degrees will be admitted directly as long as their GPA satisfies Graduate School requirements. The M.S. in Cybersecurity and Cyber Systems requires 30 credit hours. Students can select an area of study in cybersecurity or in cyber systems. For applicants lacking the required specific background, we offer conditional admission status until completing prerequisite courses. Admission to the M.S. in Cybersecurity and Cyber Systems program is based on the following factors: grade point average of 2.75 or higher on a scale of 4.0 on approximately the last 60 credit hours of undergraduate coursework, class ranking, and faculty recommendation letters. Although GRE scores are not required for admission, they are important to qualify for the High Achievers Tuition Rate. See also tuition.siuc.edu/highachievers2.html. The minimum TOEFL score requirement for international applicants is 550 (paper-based) or 80 (computer-based). The program requires a nonrefundable $65 application fee that must be submitted with the application for admissions to the M.S. program in Cybersecurity and Cyber Systems. Students must apply online and pay this fee by credit card. Please address any correspondence to “Master of Science Program in Cybersecurity and Cyber Systems,” 1230 Lincoln Drive, Southern Illinois University Carbondale, Carbondale, Illinois 62901, Mailcode 6603 or Mailcode 4511.
    [Show full text]
  • Diehard: Probabilistic Memory Safety for Unsafe Languages
    DieHard: Probabilistic Memory Safety for Unsafe Languages Emery D. Berger Benjamin G. Zorn Dept. of Computer Science Microsoft Research University of Massachusetts Amherst One Microsoft Way Amherst, MA 01003 Redmond, WA 98052 [email protected] [email protected] Abstract Invalid frees: Passing illegal addresses to free can corrupt the Applications written in unsafe languages like C and C++ are vul- heap or lead to undefined behavior. nerable to memory errors such as buffer overflows, dangling point- Double frees: Repeated calls to free of objects that have already ers, and reads of uninitialized data. Such errors can lead to program been freed undermine the integrity of freelist-based allocators. crashes, security vulnerabilities, and unpredictable behavior. We present DieHard, a runtime system that tolerates these errors while Tools like Purify [17] and Valgrind [28, 34] allow programmers to probabilistically maintaining soundness. DieHard uses randomiza- pinpoint the exact location of these memory errors (at the cost of a tion and replication to achieve probabilistic memory safety through 2-25X performance penalty), but only reveal those bugs found dur- the illusion of an infinite-sized heap. DieHard’s memory manager ing testing. Deployed programs thus remain vulnerable to crashes randomizes the location of objects in a heap that is at least twice or attack. Conservative garbage collectors can, at the cost of in- as large as required. This algorithm not only prevents heap corrup- creased runtime and additional memory [10, 20], disable calls to tion but also provides a probabilistic guarantee of avoiding memory free and so eliminate three of the above errors (invalid frees, dou- errors.
    [Show full text]